Re: GENLINMIXED EMMEANS don't agree with descriptives

Posted by Bruce Weaver on Mar 02, 2021; 3:15pm
URL: http://spssx-discussion.165.s1.nabble.com/GENLINMIXED-EMMEANS-don-t-agree-with-descriptives-tp5740214p5740236.html

Jason, I tried analyzing your sample dataset via Stata, and the same issue
arose there.  I.e., to get the predicted probabilities to match the ordinary
means, I had to omit the random intercept term from the model (using Stata's
-melogit- command).  So whatever is going on is not peculiar to GENLINMIXED.  

I'll go back to something I mentioned before:  If you are willing to model
the risk difference rather than the odds ratio, you can get GENLINMIXED to
give you predicted probabilities that match ordinary means.  But you can
also get predicted probabilities (or CI limits) that fall outside the range
0 to 1.  This is unavoidable, I think.  E.g., see this nice set of slides:

https://si.biostat.washington.edu/sites/default/files/modules/2018_SISG_4_4_0.pdf

HTH.


Beckstead, Jason-2 wrote

> Hi guys,
> Thanks for your responses regarding GENLINMIXED. I believe that including
> the random intercepts in the model is necessary to account for the nested
> structure of the data (9 binary responses per subject) and which should
> adjust the standard errors for nonindependence in the data.
> Also, because the DV is binary the binomial distribution with the logit
> link function is appropriate for conducting logistic regression. I think
> that specifying both of these options is necessary to obtain proper
> estimates of the 95% Cis for the cell means (which are proportions).
> I also note that the estimated grand mean (also a proportion) does not
> equal that of the entire sample (as calculated using MEANS or
> DESCRIPTIVES).
> At this point I am quite uneasy trusting the results from GENLINMIXED.
> Does anyone know of another way to estimate a multilevel logistic
> regression in SPSS.
> Thanks,
> Jason

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Bruce Weaver
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